Certain parts of a cartridge, in particular with a combustible sleeve, are produced from inert material. Such inert materials are provided for instance at connecting points between the driving mechanism and the projectile.
There are two decisive factors for the selection of explosive-free material. The strength of the noncombustible molded part together with the adhesives used on the tail part of the projectile to be attached has proven to be one such factor. Far more important, however, is that the inert material is flame resistant.
Noncombustible inert molded parts must be erosively removed by the mechanical effect of the weapon housings and the hot gases. This means that corresponding connecting parts, which in the case of 120 mm cartridges are known as cartridge covers, must be broken up on firing, and/or so weakened by erosion that only fragments remain. This generally takes place when there is increasing pressure and formation of hot gases in the breech area. The destroyed parts are then flushed out of the breech area and the gun barrel by the gas flow. However, the effect of the combustion gases is not always adequate, so that larger, and in particular thicker, residual pieces are left over in the breech area or may become attached to the cone piece between the breech area and the barrel. The desired removal mechanisms are counteracted, however, by the additional use of polyethanes in the molded parts to provide appropriate strength.
A further problem arises, however, from the fact that, in an ammunition container and in the assembly area of a weapon, the cartridge has at this connecting point direct contact with holding devices or the like. Under the relatively rough handling conditions of heavy cartridges and additional adverse environmental influences, vibration and associated mechanical stresses at these points can become a possible source of risk to the function of the cartridge in the breech area of the weapon. This has the consequence that the function of the weapon and safety are adversely affected, since under some circumstances the next cartridge can no longer be loaded or the smoldering residual particles of the cartridge cover could set off the next cartridge prematurely.